Sadiq Khan has spoken out following the mass shooting in New Zealand (Image: Getty Images/AP Photo/Mark Baker)

Muslims will be protected by police patrols in London after terror attacks on Mosques in New Zealand, according to the city's mayor.

Sadiq Khan has pledged to 'reassure' Muslims in London after 49 people were killed in the Kiwi city of Christchurch.

Extra patrols will take to the streets today (Friday, March 15) to keep Muslims safe.

The promise follows confirmation from the Prime Minister of New Zealand, Jacinda Ardern, that two Mosques had been targeted by terrorists in a disturbing wave of what appears to be carefully planned violence.

More than 20 people have been seriously wounded in addition to the 49 dead.

Police took three men and a woman into custody after the shootings.

Bombs were also defused at the scene of the attacks.

Sadiq Khan's statement in full

Mayor of London Sadiq Khan (Image: Kirsty O'Connor/PA Wire)

In a statement published on Twitter at 8.06am, the Mayor of London said: "Heartbreaking news from New Zealand this morning where innocent people have been murdered because of their faith.

"London stands with the people of Christchurch in the face of this horrific terror attack. London will always celebrate the diversity that some seek to destroy.

"I want to reassure the Muslim communities in London. I have been in touch with the Met Police.

"There will be highly visible policing around mosques today (March 15), as well as armed response officers, as Londoners go to pray.

"Anything suspicious should be reported to the police on 999 or the counter terror hotline on 0800 789 321."

What we know so far about one of New Zealand's 'darkest days'

A police officer talks on her phone as a roadblock near a mass shooting at a mosque in Linwood, Christchurch (Image: AP Photo/Mark Baker)

One of the four people arrested in connection with the attacks was an Australian citizen, according to Australian prime minister Scott Morrison.

Authorities in New Zealand have not elaborated on who they arrested.

But according to the Press Association, a man who claimed responsibility for the shootings left a 74-page anti-immigrant manifesto, in which he explained who he was and his reasoning for his actions.

He said he was a 28-year-old white Australian.

People were left in shock and tried to contact loved ones after the attacks (Image: AP Photo/Mark Baker)

Police Commissioner Mike Bush said police were not aware of other suspects beyond the four who were detained but they could not be certain.

"The attackers were apprehended by local police staff. There have been some absolute acts of bravery," Mr Bush said.

"I'm hugely proud of our police staff, the way they responded to this.

"But let's not presume the danger is gone."

Mr Bush said the defence force had defused a number of improvised explosive devices that were attached to vehicles stopped after the attacks.

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